On shaky ground?

Friday

Oct 5, 2012 at 12:01 AM

STOCKTON - The ground below a pump station for Stockton's $220 million Delta Water Supply Project has sunk to a dangerous level, putting the levee it sits on in "catastrophic danger" of failure, a contractor said in a scathing report presented to the city last month.

Scott Smith

STOCKTON - The ground below a pump station for Stockton's $220 million Delta Water Supply Project has sunk to a dangerous level, putting the levee it sits on in "catastrophic danger" of failure, a contractor said in a scathing report presented to the city last month.

Preston Pipelines' Sept. 7 report is filled with red flags over how the ground in the past six months has settled around the pump station at an alarming rate.

The Milpitas-based firm warned that a 54-inch pipe delivering water from the San Joaquin River into the pump station could break as the ground subsides, potentially flooding the high-tech facility and washing away the levee.

City officials dismissed Preston's warning as unfounded.

"It's not true," Robert Granberg, project director for the Delta Water Supply Project, said Thursday. He explained that the contractor has since implemented what he called a "temporary-permanent" fix at a cost of a couple of thousand dollars.

"If we don't see any more movement, we'll leave it the way it is," Granberg said. "From my perspective, this is not a catastrophic issue."

The Delta Water Supply Project, the city's most expensive capital undertaking, pumps water from the river to a purification plant 13 miles away and then to the homes of Stockton residents for drinking.

It launched in May and remains in a testing period until a long list of local, state and federal agencies sign off.

The Record obtained Preston's report through a public records request. It reveals frustration by Preston at other firms hired by the city for being slow to respond to a potential disaster.

The report warns that the city needs to "take serious consideration of the large-scale design problems that jeopardize the safety" of the pump station, which may be in "imminent danger."

To build the pump station, crews first widened the levee northwest of Stockton between the river and farmland. They next drove 120 piles 70 feet long into the ground to form a platform for the pump station.

Yet, in its first six months, the surrounding earth has sunk as much as 5 inches.

A 5-inch lip between a concrete slab on the piles and the adjacent asphalt on sunken soil outside the pump station gives a clear indication of the problem, with the pipe in a vault below ground.

City workers stopped the pump station Sept. 8 in light of the potential problem, drawing water instead from the Woodbridge Irrigation District.

The city resumed pumping - 30 million gallons a day - on Wednesday after installing two hydraulic jacks under a link in the 54-inch pipe connected on each end by a pair of flexible rubber couplings, which were off kilter. Granberg said he is satisfied.

"This was just a construction issue that got resolved," he said. "We're going to continue to operate."

City workers at the rural pump station continue to monitor the pipe with their eyes, and mechanical alarms are in place to alert them of any emergency leaks. A drainage system would send any water back into the river, he said.

Granberg said the shifting Delta is no surprise. Kleinfelder, which engineered the levee upgrade, anticipated the soil to settle as much as 6 inches.

Preston is not the only one worried about the ever-shifting Delta and the city's quick repair.

A temporary fix is likely not enough, said James Gannatal, an engineer at Proco Products, Inc., which provided the rubber couplings for the project. He wrote a letter Sept. 26 to HDR Inc., the project's design engineers.

Alan Coon, secretary-attorney for Reclamation District 2029, agreed. The city could learn from the experience of the district, which built the levee in the late 1950s and knows that temperamental corner of the Delta better than anybody, he said in a phone interview.

"Spend the money to fix it one time," he said. "It's cheaper to do it now the right way than after it's blown up."

The consequences are real, Coon said. The levee broke in the 1970s, flooding 3,000 acres of farmland and washing out an area of 20-30 acres. It took two years to drain and fix the levee and 15 years to pay off the repair.

A similar failure could jeopardize the city's new water system, he said, adding that he hopes he's wrong and the earth has settled once and for all.

"This temporary fix is a temporary fix," Coon said. "If you're going to tell us a year from now we're going to do a temporary fix every year, it won't work. It just won't."